The present disclosure relates to a sheet transport mechanism which transports a sheet-like recording medium such as paper in an image forming apparatus such as a facsimile, a copying machine, or a printer.
In the image forming apparatus such as the facsimile, the copying machine, or the printer, the sheet transport mechanism, which rotates a pair of transport rollers pressed against one pair of rollers, and nips and transports a sheet in a nip of the pair of transport rollers, is widely used as means for transporting a sheet (recording medium) such as paper, cloth, or an overhead projector (OHP) sheet.
In the above-described sheet transport mechanism, one roller of the pair of transport rollers is pressed against the other roller through a tension spring, a compression spring, or the like at a predetermined pressure. Generally, in some image forming apparatuses, one roller is pressed against the other roller by providing a separate urging member at each end of an axial direction of the pair of transport rollers.
However, in the above-described configuration, the urging member is disposed in a direction orthogonal to the axial direction of the roller so that an urging direction of the urging member is the same as a pressing direction of the roller. Here, when a short spring with a small number of turns is used to reduce a size of a width direction of the sheet transport mechanism (contact and separation directions of the pair of rollers), a spring constant is increased. Because an influence of a dimension error of a component for fixing the spring on a pressing force is increased when a spring with a large spring constant has been used, the processing force of the pair of transport rollers becomes a factor that differs between left and right of the axial direction. As a result, a sheet transporting force is uneven in the left and right of the axial direction, and becomes the cause of a skew, jam, or the like of a sheet.
In order to solve the above-described defect, for example, a sheet-material transport apparatus including one pair of transport rollers, one pair of driven rollers respectively driven by the transport rollers, one pair of pressure sections configured to press the one pair of driven rollers to the one pair of transport rollers, and a tension spring configured to extend between the pressure sections of one pair and assign a uniform pressure force to the one pair of pressure sections is proposed.